The investigation is looking into the potential culpability of drug makers in how they market and sell opioid prescription painkillers.

Sales and overdoses of prescriptions opioids have quadrupled since 1999, and nearly 2 million Americans are believe to addicted, according to Swanson's office.

"The United States is only 5 percent of the world's population, but it consumes 80 percent of the world's opioid painkillers," Swanson said in a statement. "The opioid epidemic is impacting people from all walks of life and every region of the country."

According to state data, opioid deaths in Minnesota have climbed steadily since 1999, reaching 338 in 2015.

PhRMA, a pharmaceutical trade organization, declined to comment. But the group's web site says its industry is "committed to working collectively to prevent the misuse, abuse and diversion of prescription medicines."